Means to securely fixate pacing leads and/or sensors in vessels

ABSTRACT

According to embodiments of the present invention, a cardiac lead system adapted for fixation to a vessel including an expandable fixation mechanism adapted to engage an inner surface of the vessel and a lead member comprising an anchor structure at distal end, the anchor structure configured to removably engage with fixation mechanism. Such anchor structure may be helical, and may removably engage fixation mechanism upon rotation or an application of torque, and may be extendable and/or retractable. Fixation mechanism may be polymer coated weave and/or mesh to trap anchor structure. Lead member and/or fixation mechanism may include electrodes and/or sensors, and lead member may include L-shape, S-shape, spiral, and/or sinusoidal shape for positioning of electrodes and/or sensors or for facilitated engagement of anchor structure. A guide wire attached to fixation mechanism during deployment may, prior to detachment, serve to guide lead member to a target site at fixation mechanism.

TECHNICAL FIELD

The present invention relates to implantable medical devices and, inparticular, to fixation of cardiac leads and/or sensors in a patient'svascular system.

BACKGROUND

Cardiac function management systems are used to treat arrhythmias andother abnormal heart conditions. Such systems generally include cardiacleads, which are implanted in or about the heart, for delivering anelectrical pulse to the cardiac muscle, for sensing electrical signalsproduced in the cardiac muscle, or for both delivering and sensing. Thelead typically consists of a flexible conductor, defining a centralchannel or lumen, surrounded by an insulating tube or sheath extendingfrom an electrode at the distal end to a connector pin at the proximalend.

Cardiac lead placement may be accomplished by introducing the leadthrough a major blood vessel and advancing a distal end of the lead to afinal destination in or near the heart. To facilitate cannulation of thevasculature, it is often helpful to first advance a guiding catheterthrough the desired vascular path. One difficulty with implanting leadsin this fashion is that the cardiac lead has a tendency to becomedislodged from its desired location during or after lead implantation.For example, when a clinician withdraws the guiding catheter, the leadmay dislodge or otherwise reposition. Until tissue in-growth ultimatelyfixes the lead at the desired site, cardiac leads may also becomedislodged by subsequent physiological activity.

A variety of passive means devices have been secured to cardiac leads toaffix the leads at a desired location in a patient's vasculature byexerting a radial force against vein walls. Nonetheless, there is a needin the art for a cardiac lead having a fixation mechanism whicheffectively affixes the cardiac lead at a desired position in anon-destructive manner, but which also allows the lead to berepositioned within or removed from the patient's vasculature, evenafter an extended implantation period.

SUMMARY

A cardiac lead system adapted for fixation to a vessel is provided,according to an embodiment of the present invention. The system includesan expandable fixation mechanism and a lead member. The expandablefixation mechanism includes an expanded position adapted to engage aninner surface of the vessel. The lead member has a proximal and distalends. The distal end of the lead member includes an anchor structure,which is configured to removably engage the fixation mechanism.

The anchor structure may include a helical, corkscrew, barb, tine,and/or hook configuration. Anchor structures having a helicalconfiguration may be configured to removably engage the fixationmechanism by rotating the anchor structure into the inner surface of thefixation mechanism. The fixation mechanism and/or the lead member mayinclude one or more electrodes and/or one or more sensors. Theexpandable fixation mechanism may be coated with a polymer weave and/orpolymer matrix to engage the anchor structure. The anchor structure maybe retractable into and/or extendable from the lead member.Alternatively, the anchor structure may be fixed with respect to thelead member, and the anchor structure may be exposed by extending andretracting the lead member from within a guide catheter. Alternatively,the anchor structure may be fixed with respect to the lead member, andthe anchor structure may be coated with a polyethylene glycol ormannitol for deployment.

A cardiac lead system adapted for fixation to a vessel is provided,according to another embodiment of the present invention. The systemincludes an expandable fixation mechanism and a lead member. Theexpandable fixation mechanism includes an expanded position adapted toengage an inner surface of the vessel. The lead member comprises a helixstructure, which is configured to removably engage the fixationmechanism by rotation of the helix structure into the fixationmechanism.

A method for non-destructive anchoring of a cardiac lead member to acoronary vessel is provided, according to yet another embodiment of thepresent invention. A guide wire is passed into the coronary vessel, anda stent structure is deployed over the guide wire and into the coronaryvessel. The stent structure is expanded to engage the inner surface ofthe coronary vessel. A lead member is deployed over the guide wire, thelead member including an anchor structure. According to someembodiments, the guide wire may be attached to the stent structure, andthe lead member passed over the guide wire to a “landing zone” on thestent structure prior to removal of the guide wire from the stentstructure. The anchor structure is then attached to the stent structure.The anchor structure may be helical, in which case attaching the anchorstructure to the stent structure includes rotating the anchor structureinto the stent structure. The anchor structure may also be extendedand/or retracted, and may be removed from the stent structure accordingto embodiments of the present invention.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of a cardiac rhythm management systemincluding a pulse generator coupled to a lead deployed in a patient'sheart according to one embodiment of the present invention.

FIG. 2 depicts a partial cross sectional view of a blood vessel andfixation mechanism with a side elevation view of a lead member andanchor structure, according to embodiments of the present invention.

FIG. 3 depicts a partial cross sectional view of a blood vessel andfixation mechanism and a side elevation view of a lead member attachedto the fixation mechanism via an anchor structure, according toembodiments of the present invention.

FIG. 4 illustrates a possible configuration of an anchor structure,according to embodiments of the present invention.

FIG. 5 illustrates a possible configuration of an anchor structure,according to embodiments of the present invention.

FIG. 6 illustrates a possible configuration of an anchor structure,according to embodiments of the present invention.

FIG. 7 illustrates a possible configuration of an anchor structure,according to embodiments of the present invention.

FIG. 8 illustrates a possible configuration of an anchor structure,according to embodiments of the present invention.

FIG. 9 illustrates a possible configuration of an anchor structure,according to embodiments of the present invention.

FIG. 10 depicts a partial cross sectional view of a blood vessel andfixation mechanism having a polymer coating and a side elevation view ofa lead member attached to the fixation mechanism via an anchorstructure, according to embodiments of the present invention.

FIG. 11 depicts a partial cross sectional view of a blood vessel andfixation mechanism and a side elevation view of a lead member havingmultiple electrodes and attached to the fixation mechanism via an anchorstructure, according to embodiments of the present invention.

FIG. 12 depicts a partial cross sectional view of a blood vessel andfixation mechanism and a side elevation view of an L-shaped lead memberattached to the fixation mechanism via an anchor structure, according toembodiments of the present invention.

FIG. 13 depicts a partial cross sectional view of a blood vessel andfixation mechanism and a side elevation view of another L-shaped leadmember attached to the fixation mechanism via an anchor structure,according to embodiments of the present invention.

FIG. 14 depicts a partial cross sectional view of a blood vessel andfixation mechanism and a side elevation view of a lead member havingmultiple electrodes and attached to the fixation mechanism via an anchorstructure, according to embodiments of the present invention.

FIG. 15 depicts a partial cross sectional view of a pulmonary artery andfixation mechanism and a side elevation view of a lead member having asensor and attached to the fixation mechanism via an anchor structure,according to embodiments of the present invention.

FIG. 16 depicts a partial cross sectional view of a blood vessel andfixation mechanism having a net and a side elevation view of a leadmember attached to the net via an anchor structure, according toembodiments of the present invention.

FIG. 17 depicts a partial cross sectional view of a blood vessel andfixation mechanism having an electrode and inner and outer polymerlayers and a side elevation view of a lead member attached to thefixation mechanism via an anchor structure, according to embodiments ofthe present invention.

FIG. 18 depicts a partial cross sectional view of a blood vessel,illustrating a lead member within an inner guide catheter and a fixationmechanism between the inner guide catheter and the outer guide catheter,according to embodiments of the present invention.

FIG. 19 depicts a flow chart illustrating a method for non-destructivelyanchoring a lead member to a coronary vessel.

FIG. 20 depicts a partial cross sectional view of a blood vessel,illustrating a lead member within an inner guide catheter and a fixationmechanism between the inner guide catheter and the outer guide catheter,according to embodiments of the present invention.

FIG. 21 depicts a partial cross sectional view of a blood vessel,illustrating a guide wire attached to a fixation mechanism between aninner guide catheter and an outer guide catheter.

FIG. 22 depicts a flow chart illustrating a method for non-destructivelyanchoring a lead member to a coronary vessel.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

FIG. 1 is a schematic drawing of a cardiac rhythm management system 10including a pulse generator 12 coupled to a lead member 33 deployed in apatient's heart 20 from a superior vena cava 21. As is known in the art,the pulse generator 12 is typically implanted subcutaneously at animplantation location in the patient's chest or abdomen. As shown, theheart 20 includes a right atrium 22 and a right ventricle 24, a leftatrium 26 and a left ventricle 28, a coronary sinus ostium 30 in theright atrium 22, a coronary sinus 13, and various cardiac branch vesselsincluding a great cardiac vein 14 and an exemplary branch vessel 17.

As shown in FIG. 1, lead member 33 may include an elongate body 35including a proximal region 36 and a distal region 40. The distal region40 has a distal end 42 including an electrode 44 and terminating in ananchor structure 11, according to embodiments of the present invention.Anchor structure 11 may be removably engaged with a fixation mechanism34 such as, for example, a stent structure.

To facilitate left ventricular pacing epicardially via a transveousapproach, leads 33 may be deployed in coronary veins 17 through thecoronary sinus 13. In some cases, instability of leads 33 may result inextended procedure times, re-operation, loss of capture, phrenic nervestimulation, and loss of resynchronization therapy. Development of morestable leads 33 has generally involved shapes that enable the lead 33 orthe tip of the lead 33 to push radially against the vessel 17 wallpromoting anchoring. However, for such shaped leads, dislodgement andmigration rates may remain high in some cases. For pacing anddefibrillation lead members 33 placed in the right chambers of the heart20, active fixation variants of leads have been used to penetrate theendocardium and myocardium to anchor the lead 33 in place. However, suchactively fixated leads may result in infections or may become lodgedwithin the tissue in a way that does not permit easy removal.Embodiments of the present invention provide an anchor structure 11 forsecure and removable fixation to a fixation mechanism 34, withoutpenetration of the vessel 17 wall.

Although FIG. 1 depicts lead member 33 deployed through branch vessel17, lead member 33 may alternatively be deployed through and anchoredwithin the pulmonary artery 15, according to some embodiments of thepresent invention. Furthermore, although FIG. 1 depicts lead member 33as part of a cardiac rhythm management system 10 with an electrode 44,lead member 33 may alternatively include one or more sensors and/or oneor more electrodes 44, and may couple the one or more sensors with amonitor instead of and/or in addition to pulse generator 12.

FIGS. 2-3 illustrate attachment of anchor structure 11 of lead member 33to fixation mechanism 34 according to embodiments of the presentinvention. Fixation mechanism 34 may be deployed within a vessel 31 suchas, for example, branch vessel 17 or pulmonary artery 15. Fixationmechanism 34 includes an inner surface 202 and an outer surface 204, andmay be expandable according to some embodiments of the presentinvention. FIGS. 2-3 depict fixation mechanism 34 in an expandedposition in which outer surface 204 of fixation mechanism 34 engages aninner surface 206 of vessel 31. According to some embodiments of thepresent invention, fixation mechanism 34 is a stent.

FIG. 3 depicts anchor structure 11 of lead member 33 removably engagedwith inner surface 202 of fixation mechanism 34. Anchor structure 11 maybe removably engaged with fixation mechanism 34 by turning, rotating,pushing, and/or hooking anchor structure 11 into inner surface 202,according to some embodiments of the present invention. As used herein,the term “removably engaged” is used in its broadest sense to refer toan engagement or coupling of two elements which may be reversed.Removably engaging anchor structure 11 with fixation mechanism 34substantially deters detachment and/or drifting of anchor structure 11and thus lead member 33 with respect to fixation mechanism 34, whilepermitting anchor structure 11 to be disengaged from fixation mechanism34 through a reverse application of the turning, rotating, pushing,and/or hooking force, according to some embodiments of the presentinvention. Anchor structure 11 may engage the fixation mechanism 34thereby actively fixating anchor structure 11 (and thus lead member 33)to fixation mechanism 34 but not penetrating the vessel 31 wall.

Anchor structure 11 is shown having a helical configuration in FIGS.2-3. As such, anchor structure 11 may be removably engaged with innersurface 202 of fixation mechanism 34 by rotating and/or turning theanchor structure 11 into inner surface 202. According to someembodiments of the present invention, anchor structure 11 may beremovably engaged with fixation mechanism 34 in a fashion similar to theway in which a wine bottle corkscrew may be removably engaged with acork.

FIGS. 4-9 illustrate various alternative embodiments of anchor structure11. FIGS. 4 and 5 illustrate side views of lead member 33 with an anchorstructure 11 having a helical configuration; the helix of FIG. 4 is asingle-coil helix, and the helix of FIG. 5 is a double-coil helix. FIG.6 illustrates a side view of lead member 33 with an anchor structure 11having a corkscrew configuration. According to some embodiments of thepresent invention, anchor structure 11 is a very short helix with asingle turn, extending approximately one millimeter or less from leadmember 33, and with a rounded end. FIGS. 7-9 depict side views of leadmember 33 with an anchor structure 11 having tine, hook, and barbconfigurations, respectively. Although anchor structure 11 may havevarious configurations, a helical configuration may permit simplefixation and removal through application of torque. Based on thedisclosure provided herein, one of ordinary skill in the art willrecognize that various alternative configurations of anchor structure 11may be utilized to achieve results similar to those achievable with theconfigurations of FIGS. 4-9; for example, the helical configurations ofFIGS. 4-5 may be arranged for engagement with either clockwise orcounterclockwise rotation of anchor structure 11 into fixation mechanism34.

FIG. 10 illustrates a fixation mechanism 34 having a polymer coating1002 for inner layer 202, according to embodiments of the presentinvention. Anchor structure 11 may removably engage with fixationmechanism 34 by being driven into polymer coating 1002 such as, forexample, through the application of torque or other turning force.According to some embodiments of the present invention, polymer layer1002 is a DACRON® or expanded polytetrafluoroethylene (ePTFE) weave orpolymer matrix. Anchor structure 11 may engage the polymer layer 1002thereby actively fixating anchor structure 11 (and thus lead member 33)to fixation mechanism 34 but not penetrating the vessel 31 wall.

FIG. 11 depicts a lead member 33 having multiple electrodes 1102 spacedat intervals along lead member 33, according to embodiments of thepresent invention. Lead member 33 may have a sinusoidal, spiral, orother non-linear shape, as depicted, to permit electrodes 1102 tocontact the inner surface 206 of vessel 31 when anchor structure 11 isengaged with fixation mechanism 34. According to some embodiments of thepresent invention, lead member 33 is initially substantially straightand then assumes the depicted sinusoidal, spiral, or other non-linearshape upon removal of a stylet and/or guide wire from lead member 33.

FIG. 12 illustrates a lead member 33 having a bend 1202 which creates anL-shape lead member 33 according to embodiments of the presentinvention. Such an L-shape configuration permits anchor structure 11 toprotrude at an angle from the longitudinal axis of lead member 33(instead of in-line with lead member 33) which, in turn, may facilitateengagement of anchor structure 11 with fixation mechanism 34. Accordingto some embodiments of the present invention, lead member 33 isinitially substantially straight and then assumes the depicted L-shapeupon removal of a stylet and/or guide wire from lead member 33.

In a similar fashion, FIG. 13 illustrates a lead member 33 having a headportion 1302 which permits anchor structure 11 to protrude at an anglefrom the longitudinal axis of lead member 33. Anchor structure 11 mayprotrude at a substantially right angle from the longitudinal axis oflead member 33, for example. According to some embodiments of thepresent invention, head portion 1302 may be shaped with rounded edges tofacilitate deployment of lead member 33 through vessel 31. According tosome embodiments, anchor structure 11 is fixed and may be coated with adissolvable substance to prevent anchor structure 11 from catching ordamaging a patient's vasculature during deployment of lead member 33.

FIGS. 14 and 15 depict various alternative uses of a lead member 33anchored to a fixation mechanism 34 according to embodiments of thepresent invention. FIG. 14 depicts a lead member 33 having multipleelectrodes 1402 spaced at intervals along lead member 33. Use ofmultiple lead member 33/fixation mechanism 34 combinations in heart 20may permit a series of electrodes to be available to optimizesynchronization and mitigate issues such as high pacing thresholds anddiaphragmatic stimulation. According to some embodiments of the presentinvention, anchor structure 11 and distal tip 1404 of lead member 33 areelectrically inactive and/or insulated and provide anchoring and/orfixation for lead member 33. According to other embodiments, anchorstructure 11 and/or distal tip 1404 are electrically active and areconfigured to energize a metallic and/or conductive fixation mechanism34 which, in turn, may operate electrodes and/or sensors contained onand/or within fixation mechanism 34.

FIG. 15 depicts a lead member 33 having a pressure sensor module 1502and deployed in the pulmonary artery 15. According to some embodimentsof the present invention, fixation mechanism 34 permits adequate bloodflow through pulmonary artery 15 after deployment. Pressure sensor 1502may be used to evaluate decompensation, for example. Attaching leadmember 33 to fixation mechanism 34 in pulmonary artery 15 permitsplacement of sensors within lead member 33 and/or fixation mechanism 34without injuring or damaging the relatively fragile pulmonary artery 15,according to embodiments of the present invention.

FIG. 16 illustrates a lead member 33 with an anchor structure 11removably engaged with a net 1602. Net 1602 connects at least two pointsalong inner surface 202 of fixation mechanism 34. According to someembodiments of the present invention, net 1602 is a polymer layer of aDACRON® or expanded polytetrafluoroethylene (ePTFE) weave or polymermatrix deployed in a net-like fashion across the diameter of innersurface 202. According to some embodiments of the present invention, apore size of net 1602 is optimized to enable blood flow, although net1602 may also include multiple layers to trap and fixate anchorstructure 11 whether anchor structure 11 includes the helixconfiguration of FIGS. 4-5, the corkscrew configuration of FIG. 6, orthe barb/tine/hook configurations of FIGS. 7-9. Net 1602 may alsoinclude a metallic and/or conductive structure, such as interlaced metalwires, to provide energization of a metallic and/or conductive fixationmechanism 34 which, in turn, may operate electrodes and/or sensorscontained on and/or within fixation mechanism 34.

FIG. 17 depicts a fixation mechanism 34 having a first polymer coating1002 for inner layer 202 and a second polymer coating 1704 for outerlayer 204 of fixation mechanism 34. According to some embodiments of thepresent invention, polymer layers 1002 and/or 1704 are a DACRON® orexpanded polytetrafluoroethylene (ePTFE) weave or polymer matrix. Outersurface 204 contacts inner surface 206 of vessel 31, and according tosome embodiments, polymer layer 1704 acts as an electrical insulatorbetween fixation mechanism 34 and inner surface 206 of vessel 31.

Fixation mechanism 34 includes a metallic and/or conductive layer 1701between polymer layers 1002, 1704. According to some embodiments of thepresent invention, a gap 1706 formed in polymer layer 1704 permits apoint electrode 1702 to protrude from metallic layer 1701 and againstinner surface 206 of vessel 31. Anchor structure 11 may be electricallyactive to energize fixation mechanism 34, and thus may provideelectrical impulses to vessel 31 via electrode 1702 when anchorstructure 11 of lead member 33 is removably engaged with fixationmechanism 34. According to some embodiments of the present invention,polymer layer 1002 is insulative, and an electrically active anchorstructure 11 penetrates polymer layer 1002 to engage with conductivelayer 1701. Preferential orientation of electrodes 1702 could occuralong the heart 20 wall.

FIGS. 18-20 illustrate a method for non-destructive anchoring of leadmember 33 to coronary vessel 31 according to embodiments of the presentinvention. FIG. 19 depicts a flow chart 1900 showing a method ofanchoring lead member 33 to vessel 31 according to one embodiment of thepresent invention. A guide wire 50 is passed through the patient'svasculature and into coronary vessel 31 (block 1902). Lead member 33 maybe pre-loaded over an inner guide catheter 58 such that fixationmechanism 34 is in a compressed position between inner guide catheter 58and outer guide catheter 60. Fixation mechanism 34, such as the stentstructure depicted in FIG. 18, may then be deployed over guide wire 50and into coronary vessel 31 (block 1904) by deploying the inner guidecatheter 58 and outer guide catheter 60 over guide wire 50. Inner guidecatheter 58 is then pushed in a distal direction with respect to outerguide catheter 60, or outer guide catheter 60 is then pulled in aproximal direction with respect to inner guide catheter 58, such thatfixation mechanism 34 deploys to an expanded position (block 1906) shownin FIGS. 2-3 and 10-17, such that fixation mechanism 34 engages innersurface 206 of vessel 31.

Lead member 33 and anchor structure 11 may also be deployed over guidewire 50 (block 1908), either at the same time as fixation mechanism 34or subsequent to deployment of fixation mechanism 34. According to someembodiments of the present invention, anchor structure 11 is extendableand/or retractable. If anchor structure 11 is extendable, anchorstructure 11 may then be extended from lead member 33 and/or inner guidecatheter 58 (block 1912). Anchor structure 11 may be attached tofixation mechanism 34 (block 1910); for example, a helical anchorstructure 11 may be attached to fixation mechanism 34 by applying torqueto anchor structure 11 to drive anchor structure 11 into fixationmechanism 34 as depicted in FIGS. 3 and 10-17. According to someembodiments of the present invention, deploying fixation mechanism 34between outer guide catheter 60 and inner guide catheter 58 may serve toprevent premature snagging of anchor structure 11 on fixation mechanism34.

FIGS. 21 and 22 illustrate an alternative method for non-destructiveanchoring of lead member 33 to coronary vessel 31 according toembodiments of the present invention. FIG. 22 depicts a flow chart 2200showing a method of anchoring lead member 33 to vessel 31 according toone embodiment of the present invention. A first guide wire may bepassed into coronary vessel 31 (block 2202), and a second guide wire2104 may be attached to a stent structure 34 at a target site 2102(block 2204). According to some embodiments of the present invention,guide wire 2104 may be designed to be broken away or snapped off offixation mechanism 34 subsequent to deployment of lead member 33. Stentstructure 34 may be deployed over the first guide wire into coronaryvessel 31 (block 2206), and expanded to engage an inner surface ofcoronary vessel 31 (block 2208). Such expansion may be achieved with aself-expanding stent structure 34 and/or with balloon expansion of stentstructure 34, for example. Lead member 33, along with anchor structure11, may be navigated over the second guide wire 2104 to the target site2102 (block 2210). According to some embodiments of the presentinvention, the second guide wire 2104 is then detached from the stentstructure 34 (block 2212) and the anchor structure 11 is attached tostent structure 34 (block 2214). Alternatively, anchor structure 11 maybe attached to stent structure 34 (block 2216) prior to detachment ofsecond guide wire 2104 from stent structure 34 (block 2218). Accordingto some embodiments of the present invention, guide wire 2104 may beJ-shaped near target site 2102 to prevent premature snagging of anchorstructure 11 on fixation mechanism 34 prior to anchor structure 11reaching the vicinity of target site 2102.

According to some embodiments of the present invention, anchor structure11 is rigidly or semi-rigidly fixed on distal tip 1404, and torque isapplied to anchor structure 11 by rotating lead member 33. For example,lead member 33 may be rotated within inner guide catheter 58, and innerguide catheter 58 may serve to help balance and position lead member 33prior to and during rotation. Anchor structure 11 may be positioned inthe vicinity of an inner surface 202 of fixation mechanism 34 androtated and/or translated until an end of anchor structure 11 catchesand penetrates fixation mechanism 34. According to such embodiments,extending anchor structure 11 includes extending lead member 33 fromwithin inner guide catheter 58 to expose anchor structure 11. Accordingto some embodiments of the present invention, an anchor structure 11which is rigidly or semi-rigidly fixed on distal tip 1404 may be coatedwith a smooth dissolvable compound, such as a polyethylene glycol ormannitol, to facilitate deployment of lead member 33 through thepatient's vasculature.

Anchor structure 11 is removable, according to embodiments of thepresent invention. Reasons for removal of lead member 33 and anchorstructure 11 may include lack of response to a therapy, inadequatepressure reading, or infection associated with the wound site associatedwith pulse generator 12 or with the vascular access site, for example.In some cases, anchor structure 11 may be removed and re-anchored and/orre-implanted. In other cases, such as cases in which it is recommendedthat all links to the pulse generator 12 pocket area be removed, anchorstructure 11 and lead member 33 may be completely removed from thepatient. Anchor structure 11 may optionally be removed from fixationmechanism 34 (block 1914); for example, an anchor structure 11 having ahelical configuration may be removed from fixation mechanism 34 byapplying a torque to the anchor structure 11 opposite to the torque usedto engage anchor structure 11 with fixation mechanism 34. Such a reverseturning, rotation, and/or application of torque may serve to “unscrew”and/or “unthread” anchor structure 11 from fixation mechanism 34. Ifanchor structure 11 is retractable, anchor structure 11 may be retracted(block 1916) for facilitated removal from the patient through thepatient's vasculature. According to some embodiments of the presentinvention, fixation mechanism 34 is non-removable; however, fixationmechanism 34 may be made and used to feature no direct linkage via alumen in the lead 33 or sensor between an infection site and fixationmechanism 34, such that abandoning fixation mechanism 34 may not be aconcern.

According to embodiments of the present invention, guide wire 50 may bea stylet configured to substantially straighten lead member 33. A distalend of lead member 33 may be configured to assume an S-shape (asdepicted in FIGS. 3, 10, 14, 15, 17), a sinusoidal or spiral shape (asdepicted in FIG. 11), and/or an L-shape (as depicted in FIGS. 12-13) inthe absence of a reinforcing stylet 50, for example. According to suchembodiments, stylet 50 may be removed after engagement of anchorstructure 11 with fixation mechanism 34 to permit lead member 33 toassume a desired configuration; alternatively, stylet 50 may be removedprior to engagement of anchor structure 11 with fixation mechanism 34 toachieve a desirable angle of anchor structure 11 with respect tofixation mechanism 34 to facilitate engagement of anchor structure 11 tofixation mechanism 34.

According to other embodiments of the present invention, anchorstructure 11 is movable with respect to lead member 33. FIG. 20 depictsone such embodiment with a lead member 33 having a drive shaft 1902coupled with anchor structure 11 through a hole 2004 in distal tip 1404.According to such embodiments, torque may be applied to anchor structure11 by applying torque to drive shaft 2002, which moves substantiallyindependently relative to lead member 33. According to some embodimentsof the present invention, anchor structure 11 is retractable into leadmember 33 by pulling and/or rotating drive shaft 2002 to bring anchorstructure 11 into lead member 33 through hole 2004, and is extendablefrom lead member 33 by pushing and/or rotating drive shaft 2002 to bringanchor structure 11 out of lead member 33 through hole 2004. Accordingto some embodiments of the present invention, anchor structure 11maintains a substantially straight configuration when retracted withinlead member 33 and assumes a configuration similar to a configurationdepicted in FIGS. 4-9 when extended from lead member 33. Such a dynamicconfiguration may be achieved, for example, by imparting anchorstructure 11 with a memory. According to alternative embodiments of thepresent invention, an extendable-retractable mechanism could be utilizedwhich keeps anchor structure 11 (such a helical anchor structure 11)inside lead member 33 until exposure is desired by either rotating driveshaft 2002 or a stylet or by turning a terminal pin and activating athreaded or post-style advancement mechanism.

Drive shaft 2002 may also be flexible, to permit use of a drive shaft2002 and anchor structure 11 combination with embodiments of lead member33 such as those depicted in FIGS. 12 and 13. Drive shaft 2002 maysimply bend at bend 1202 or at head 1302 to transform a torque about thelongitudinal axis of lead member 33 to a torque about the longitudinalaxis of anchor structure 11. Alternatively, head 1302 may, for example,include a type of universal joint to otherwise transform a torque aboutthe longitudinal axis of lead member 33 to a torque about the axis ofanchor structure 11.

Embodiments of the present invention utilize relatively straightforwardimplant techniques, feature positional stability, and offer ease ofremoval for lead members 33. Fixation mechanism 34 may be self-expandingor balloon deployable, according to embodiments of the presentinvention. Fixation mechanism 34 may also have very clear radiographicfeatures to facilitate deployment, according to some embodiments.According to some embodiments of the present invention, fixationmechanism 34 is made with a nitinol, stainless steel, shape memoryalloys, polymers, and/or cobalt chromium. According to some embodimentsof the present invention, fixation mechanism 34 may be electricallyactive and may be made with or include a nickel or platinum alloy.According to some embodiments of the present invention, fixationmechanism 34 and/or outer layer 1704 may be made with a material, suchas, for example, a mesh or porous material, which facilitates in-growthof tissue into fixation mechanism 34 and/or of fixation mechanism 34into tissue; for example, fixation mechanism 34 may include a Gore®- orePTFE-type material. According to some embodiments of the presentinvention, anchor structure 11 may be made with a metal, polymer, alloy,or other suitable material which gives anchor structure 11 enoughstrength and rigidity to puncture and/or engage with fixation mechanism34 or with a fabric weave or mesh of fixation mechanism 34 and to retainengagement therewith until intentionally removed.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

I claim:
 1. A cardiac lead system adapted for fixation to a vessel, thesystem comprising: an expandable fixation mechanism having an expandedposition adapted to engage an inner surface of the vessel; and a leadmember having a proximal end and a distal end, the distal end comprisinga helix structure, wherein the helix structure removably engages thefixation mechanism by rotation of the helix structure into the fixationmechanism.
 2. The system of claim 1, wherein the helix structurecomprises a single-coil configuration.
 3. The system of claim 1, whereinthe inner surface of the vessel is a first inner surface, wherein thefixation mechanism comprises: an outer surface adapted to engage thefirst inner surface; a second inner surface; and a net connecting atleast two points along the second inner surface, and wherein the helixstructure is configured to removably engage the fixation mechanism byrotation of the helix structure into the net.
 4. The system of claim 1,wherein the inner surface of the vessel is a first inner surface,wherein the fixation mechanism comprises: an outer surface adapted toengage the first inner surface; and a second inner surface comprising acoating of polymer, and wherein the helix structure is configured toremovably engage the fixation mechanism by rotation of the helixstructure into the coating of polymer.
 5. The system of claim 4, whereinthe coating of polymer is a polymer weave structure.
 6. The system ofclaim 4, wherein the coating of polymer is a polymer mesh structure. 7.The system of claim 4, wherein the coating of polymer is a first coatingof polymer, the outer surface comprising a second coating of polymer. 8.The system of claim 7, wherein the helix structure is electricallyactive, wherein the second coating of polymer includes at least one gap,wherein the fixation mechanism further comprises at least one electrodeconfigured to contact the first inner surface through the at least onegap, wherein the fixation mechanism comprises a metallic structure incontact with the at least one electrode, and wherein the helix structureis configured to removably engage the fixation mechanism by rotation ofthe helix structure into the metallic structure through the firstcoating of polymer.
 9. The system of claim 4, wherein the polymer isselected from the group consisting of: DACRON®, expandedpolytetrafluoroethylene, and Teflon®.
 10. The system of claim 1, whereinthe helix structure removably engages the fixation mechanism by rotationof the helix structure into the fixation mechanism without penetratingthe inner surface of the vessel.
 11. A cardiac lead system adapted forfixation to a vessel, the system comprising: an expandable fixationmechanism having an expanded position adapted to engage an inner surfaceof the vessel; and a lead member having a proximal end and a distal end,the distal end comprising an anchor structure, wherein the anchorstructure is substantially rigid and removably engages the fixationmechanism by penetrating the fixation mechanism.
 12. The system of claim11, wherein the fixation mechanism is a stent.
 13. The system of claim11, wherein the anchor structure comprises a helical configuration. 14.The system of claim 13, wherein the anchor structure protrudeslongitudinally from the lead member, and wherein the anchor structure isconfigured to removably engage the fixation mechanism by rotating theanchor structure into the fixation mechanism.
 15. The system of claim11, wherein the anchor structure comprises a configuration selected fromthe group consisting of: a hook configuration, a tine configuration, abarb configuration, and a corkscrew configuration.
 16. The system ofclaim 11, wherein the lead member comprises at least one electrode. 17.The system of claim 16, wherein the at least one electrode is amultiplicity of electrodes, and wherein each of the multiplicity ofelectrodes is spaced at an interval along the lead member.
 18. Thesystem of claim 17, wherein at least a portion of the lead membercomprises a substantially sinusoidal shape to permit the multiplicity ofelectrodes to contact the inner surface of the vessel at differentlocations.
 19. The system of claim 11, wherein the fixation mechanism iselectrically conductive and comprises at least one electrode in contactwith the inner surface, and wherein the anchor structure is electricallyactive.
 20. The system of claim 11, wherein the anchor structure isextendable from within the lead member.
 21. The system of claim 20,wherein the anchor structure is retractable back into the lead member.22. A cardiac lead system adapted for fixation to a vessel, the systemcomprising: an fixation mechanism having an inner surface, an outersurface, and an expanded position in which the outer surface of thefixation mechanism engages an inner surface of the vessel; and a leadmember having a proximal end and a distal end, the distal end comprisingan anchor structure, wherein the anchor structure removably engages theinner surface of the fixation mechanism by penetrating the fixationmechanism.
 23. The system of claim 22, wherein the fixation mechanism isa stent.
 24. The system of claim 22, wherein the anchor structurecomprises a helical configuration.
 25. The system of claim 22, whereinthe anchor structure protrudes from the lead member, and wherein theanchor structure is configured to removably engage the fixationmechanism by rotating the anchor structure into the fixation mechanism.